1. Field of Invention
The present invention relates to a photolithographic process. More particularly, the present invention relates to an electron beam photolithographic process that can prevent charge accumulation.
2. Description of Related Art
As dimensions of a semiconductor device is reduced to the sub-micron range, electron beam photolithographic techniques have to be employed. This is because an electron beam has a smaller wavelength (about 13.5 nm). Unlike optical photolithographic techniques, the resolution of an electron beam is not limited by diffraction. However, an electron beam is limited by electron dispersion on the surface of an object as well as aberration control of optical direction and shape. In general, electron beam photolithographic technique involves the production of a photomask and the transfer of pattern from the photomask to a photoresist layer on a substrate.
One major problem for using electron beam in photolithographic process is the accumulation of electric charges in the photoresist layer. To form a pattern on a substrate using an electron beam, a photoresist layer is first formed over a substrate. The photoresist layer is selectively exposed by an electron beam. Through exposure to the electron beam, physical and chemical properties of the photoresist material are changed. Regions subjected to electron beam radiation will become soluble or insoluble, depending on the photoresist material chosen. Thereafter, a chemical developer is applied to react with the exposed or unexposed photoresist material so that the exposed or unexposed photoresist layer is removed. The residual resist layer can subsequently be used as a protective mask for etching or ion implantation operation.
In general, photoresist is made from a hard polymeric material having high insulation capability. When an electron beam shines on the surface of a photoresist layer, electric charges produced by the electron beam will accumulate on the photoresist surface creating an electric field, thereby distorting the electron beam close to the surface. Since a narrow beam of smaller than 13.5 nm is often used in electron beam photolithography, the accumulation of minute electric charges on the surface can result in considerable beam distortion. Any distortion of the electron beam may lead to loss in precision, errors in pattern and extension inaccuracy.
Accordingly, one object of the present invention is to provide an electron beam photolithographic process for patterning an insulation layer over a substrate. First, a conductive photoresist layer having a conjugate structure is formed over the insulation layer. An electron beam photolithographic process is conducted using a photomask so that the pattern on the photomask is transferred to the conductive photoresist layer. Alternatively, the pattern is transferred by directly using the electron beam without any mask.
The conductive polymer having a conjugate structure is able to form a mutual conjugate bonding structure and the electrons within the material are in a dynamic resonance state. Hence, when an electron beam is used in a photolithographic process, electric charges accumulated on the photoresist layer can be rapidly conducted away by the resonance effect in the conjugate structure of the conductive polymer. Without the accumulation charges on the photoresist layer, electron beam distortion will not occur and resolution of electron beam photolithography can be maintained.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.